Human tears are capable of inhibiting the activity of the thiol protease, papain. This inhibitory activity has been found in the tears of all volunteers tested. It has also been found in rabbit tears and ocular tissues. We propose to characterize the inhibitor found in tears and to isolate and purify the inhibitory activity from ocular tissues. To clarify the function of this inhibitor, we are also isolating proteolytic enzymes from ocular tissues and measuring their susceptibility to the inhibitor. Inhibitor concentrations in tear samples of patient with ocular disease will be measured to determine if there is any relationship between disease and inhibiting activity. Proteolytic inhibitors may be important in the control of ocular ulceration, neovascularization and other inflammatory processes.